Battery packs that are mounted on apparatuses, vehicles or the like are configured by combining a plurality of storage batteries in series or parallel in order to obtain a voltage or capacity needed for the apparatuses. Across output terminals of the battery pack, a load such as a semiconductor device or an electric motor is connected via a device such as a voltage converter. In situations where a high voltage is needed in accordance with requirements of the load or where low current is used to obtain necessary electric power, storage batteries are connected in series thereby increasing a voltage of the battery pack. In situations where an apparatus needs to be operative for a long period of time, the number of parallel rows of storage batteries is increased to augment the capacity. In this way, a combination of series/parallel connection is determined according to factors such as requirements of apparatuses or the like that serves as loads.
Many ideas have been proposed for a battery pack. In, for instance, Patent Reference 1, it is described that in a process where a plurality of storage batteries fabricated is assembled into a battery pack, a minimum capacity battery is selected for control operation, and as a representative of the batteries in the battery pack. In Patent Reference 2, an idea is incorporated by which an over-discharged battery in a battery pack is detected early.
One problem with a battery pack lies in that when an external short-circuit occurs in an apparatus connected to the battery pack, the short circuit current causes the storage batteries to be heated and thereby damaged.
To take measures, conventionally a thermistor, a voltage sensing circuit and the like that achieve a current interruption capability to ensure safety is provided in an electric power storage system that uses the battery pack, and current interruption capability is incorporated that interrupts an electric current circuit in response to a control signal.
For instance, a small type battery pack such as in a portable device, if used, produces less current and its switch for operating in an emergency is also of small type; thus, it is sufficiently possible to cause the small type battery pack to have the current interruption capability such as above.